The present invention relates to reducing the harmonic noise generated by a propulsion motor control chopper apparatus in relation to receiving the input control signal frequencies for a transit vehicle, such as are provided for vehicle detection and control within individual track signal blocks as described in an article published in the Westinghouse Engineer for September 1972 at pages 145 to 151. The input speed command signals at known frequencies are received from the roadway track circuit signal blocks and pass through bandpass filters to detect the respective one and zero portions of the speed command as disclosed in U.S. Pat. No. 3,810,161 of A. P. Sahasrabudhe. A suitable bandpass filter per se is shown in U.S. Pat. No. 4,016,517 of Sahasrabudhe and Matty. Propulsion motors have been controlled by a software program controlled microprocessor as disclosed in U.S. Pat. Nos. 4,090,115 of J. H. Franz, 4,095,153 of T. C. Matty and J. H. Franz, and 4,123,693 of L. W. Anderson and J. H. Franz.
In an article entitled "Propulsion Control for Passenger Trains Provides High Speed Service" that was published in the Westinghouse Engineer for September 1970 at pages 143 to 149 there is discussed the operation of the p signal to establish the requested tractive effort of the vehicle.
It is desired that a fixed average frequency control of the propulsion motor current determining chopper apparatus be provided, since by experience this gives a reliable propulsion motor operation in relation to average heating characteristics of the motors and the associated chopper apparatus. This fixed frequency of the chopper apparatus provides known harmonic sidebands in regard to the control signal bandpass filters for sensing the input control signalling frequencies.